1. Field of the Invention
The present invention relates to multiple channel communication systems, and more particularly, to a device and a method for configuring a digital phase-locked loop (PLL) to recover loop timing of data received over multiple channel communication systems.
2. Description of the Related Art
Digital Subscriber Line (xDSL) technology refers to receiving and transmitting technology for data transmission between digital subscriber loop (DSL) modems. Generally, xDSL technology includes High-speed Digital Subscriber Lines (HDSLs), Symmetric High-speed Digital Subscriber Lines (SHDSLs), Asymmetric Digital Subscriber Lines (ADSLs), Splitterless ADSLs, and Very-high-speed Digital Subscriber Lines (VDSLs).
Multiple channel communication systems such as conventional xDSL have a master-slave configuration, and transmit a specific reference signal used for synchronization, from a central processing office, i.e., the master, to a user terminal, i.e., the slave. Usually, in multiple communication systems, loop timing for transmitting and receiving correct data between the user terminal and the central processing office has to be guaranteed. Typically, when the central processing office operates as the master and a reference signal having a specific frequency (or a particular channel specifically assigned for only a PLL operation, as distinguished from a data transmission channel) is output to the user terminal, the user terminal receives the reference signal and performs the PLL operation to extract the timing information from the received signal.
The performance of the PLL operation is very important in terms of performance and reliability of the overall system. Thus, an accurate PLL operation has to be carried out and the user terminal has to perform the PLL operation depending entirely on the received reference signal.
In a multiple channel environment, even if the same PLL is operated, its function differs with the channel environment of the communication system to which it is applied. This is because attenuation of the reference signal is present due to interference with other communications systems transferring signals on the same signal line, or due to channel noise. With lowered signal reliability of the received signal, inaccurate PLL operation in the receiving stage can result.